And escape could have been easy for Edmond and the priest
All they had to do was not give their food bowl, then one of them had to lay on the floor pretending to be dead when the guard looks in, and the other hides out of site. When the guard comes in, they both jump him and either kock him out or kill him. Then they can try to get out.
Even if multiple guards came in, they had a chance of overpowering them, once the priest trained Edmond to fight. And they could probably take on any guard they encounter trying to leave.